Django constructs redirect URLs as https only if request.is_secure() is true.

And that evaluates to true if either uwsgi sets wsgi.url_scheme to https, or
if the request header contains a key + value configured as a tuple in
settings.SECURE_PROXY_SSL_HEADER

As some parts might be accessed over plain http and some over https (if Apache
exposes both ports), the easiest is to:

* Use the conventional header:

        X-Forwarded-SSL: on

* Set this header from Apache SSL VirtualHost

* Configure Django to check for this header with:

        SECURE_PROXY_SSL_HEADER = ('X-Forwarded-SSL', 'on')

As this is an essential security setting that shouldn't need additional tweaks,
adding the setting to settings.py (and not local_settings.py).

Without this fix, the login form at /admin/ would upon successful login
redirect to plain http, even when accessed over https.